CAREER: Influence of Pressure on Surfactant Thermodynamics and Transport

Drexel University, Philadelphia PA

Investigators

Abstract

Water is a desirable and important solvent for many reasons. Water has low toxicity, low vapor pressure, and high solubility for many compounds. However, water is becoming increasingly limited and expensive as a resource. For example, we currently use more than 2 million gallons of water for each hydraulically fracked well, which requires costly water treatment to remove contaminants. This is equivalent to 40,000 baths, an amount of water that is raising serious concern in arid American states. Due to these environmental concerns, the use of supercritical CO2 fracking fluids is an important research area. Supercritical CO2 systems have extraordinary potential to reduce water use and greatly reduce the environmental impact of current and next-generation industrial processes. In many of these processes, molecules called surfactants are also vital to their use. Surfactants lower the surface tension between two liquids or between a liquid and a solid. Surfactants affect the transport of fluids in these complex environments involving oil, water, gases, and solids. However, very little is known regarding their effect at high pressure. This lack of understanding is slowing major strides in the use of CO2 as a "green" alternative solvent in separations, in chemical reactions, medical device fabrication, and hydrocarbon fracking fluids. The principal investigator has recently developed and demonstrated an instrument to accurately measure properties of surfactants at high pressure interfaces and surfaces and understand how chemical structure influences performance. This award will focus on developing thermodynamic and transport models describing surfactant interfacial activity at high pressure interfaces via a newly developed high pressure microtensiometer and analysis technique. Model parameterization will result from analyzing static and dynamic interfacial tension data of various surfactants at various interfaces as a function of pressure and temperature. This work will be highly facilitated by a time scale analysis taking into account the effect of interfacial curvature, surfactant concentration, and bulk fluid flow, which allows for the distinction between kinetic and diffusion transport mechanisms. Several chemistry/performance correlations are expected. For example, quantification of partition coefficients in various phases will determine the preferential solubility of different chemical structures and their applicability in high pressure processes. Interfacial rheology studies will allow for better understanding of foam and emulsion stability as a function of chemical structure and interfacial activity. A theoretical framework that combines kinetic theories and thermodynamic equations of state models will guide design of improved molecular architectures. The model parameters generated by this work will allow for (1) a deeper understanding of surfactant thermodynamics at elevated pressures (2) a direct correlation between transport parameters and surfactant structure and ultimately (3) correlation between molecular structure and performance in industrial applications. Educationally, this funded work in partnership with the Lindy Scholars Program and the Upper Darby School District, will develop a STEM CAREER path building program involving five diverse elementary/middle schools. In collaboration with the Louis Stokes-Alliance for Minority Participation, we will introduce and prepare under-represented minorities for research training during their Drexel tenure. Lastly, the PI will hold annual industrial workshops, inviting local industries, to share in recent discoveries and experimental findings in an effort to build collaboration and increase the dissemination of fundamental knowledge and understanding. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.